ame from the two opposite seed leaves or cotyledons with which
the young plant is furnished. These leaves are usually quite different
in shape from the other leaves, and not infrequently are very thick
and fleshy, filling nearly the whole seed, as may be seen in a bean or
pea. The number of the dicotyledons is very large, and very much the
greater number of living spermaphytes belong to this group. They
exhibit much greater variety in the structure of the flowers than the
monocotyledons, and the leaves, which in the latter are with few
exceptions quite uniform in structure, show here almost infinite
variety. Thus the leaves may be simple (undivided); _e.g._ oak, apple;
or compound, as in clover, locust, rose, columbine, etc. The leaves
may be stalked or sessile (attached directly to the stem), or even
grown around the stem, as in some honeysuckles. The edges of the
leaves may be perfectly smooth ("entire"), or they may be variously
lobed, notched, or wavy in many ways. As many of the dicotyledons are
trees or shrubs that lose their leaves annually, special leaves are
developed for the protection of the young leaves during the winter.
These have the form of thick scales, and often are provided with
glands secreting a gummy substance which helps render them
water-proof. These scales are best studied in trees with large, winter
buds, such as the horsechestnut (Fig. 92), hickory, lilac, etc. On
removing the hard, scale leaves, the delicate, young leaves, and often
the flowers, may be found within the bud. If we examine a young shoot
of lilac or buckeye, just as the leaves are expanding in the spring, a
complete series of forms may be seen from the simple, external scales,
through immediate forms, to the complete foliage leaf. The veins of
the leaves are almost always much-branched, the veins either being
given off from one main vein or midrib (feather-veined or
pinnate-veined), as in an apple leaf, or there may be a number of
large veins radiating from the base of the leaf, as in the scarlet
geranium or mallow. Such leaves are said to be palmately veined.

[Illustration: FIG. 92.--End of a branch of a horsechestnut in winter,
showing the buds covered by the thick, brown scale leaves, x 1.]

Some of them are small herbaceous plants, either upright or prostrate
upon the ground, over which they may creep extensively, becoming
rooted at intervals, as in the white clover, or sending out special
runners, as is seen in the strawb